Dyuichi Blog

javaimport java.util.ArrayList;
import java.util.List;

// Iterator Interface
interface Iterator<T> {
    boolean hasNext();
    T next();
}

// Aggregate (Collection) Interface
interface Aggregate<T> {
    Iterator<T> iterator();
}

// Concrete Iterator
class ConcreteIterator<T> implements Iterator<T> {
    private List<T> list;
    private int cursor;

    public ConcreteIterator(List<T> list) {
        this.list = list;
        this.cursor = 0;
    }

    @Override
    public boolean hasNext() {
        return cursor != list.size();
    }

    @Override
    public T next() {
        T obj = null;
        if (this.hasNext()) {
            obj = this.list.get(cursor++);
        }
        return obj;
    }
}

// Concrete Aggregate
class ConcreteAggregate<T> implements Aggregate<T> {
    private List<T> list;

    public ConcreteAggregate() {
        this.list = new ArrayList<>();
    }

    public void add(T obj) {
        this.list.add(obj);
    }

    @Override
    public Iterator<T> iterator() {
        return new ConcreteIterator<>(this.list);
    }
}

// Client
public class IteratorPattern {
    public static void main(String[] args) {
        ConcreteAggregate<String> aggregate = new ConcreteAggregate<>();
        aggregate.add("A");
        aggregate.add("B");
        aggregate.add("C");

        Iterator<String> iterator = aggregate.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}